The invention relates generally to a polymeric radial shaft sealing ring and, more particularly, to one of the type having a sealing axis and a sealing lip that contacts the periphery of a shaft with respect to which it provides a seal; the sealing lip is further provided with ribs that are evenly distributed in the circumferential direction and which project radially inwardly.
This general type of radial shaft sealing ring is disclosed by the German Patent 28 35 359, which corresponds to U.S. Pat. No. 4,283,064 (the contents of which are herein incorporated by reference). The reference discloses a radial shaft sealing ring for hydrodynamic shaft seals that has ribs which project radially towards the inside only when the sealing ring is in a relaxed state. During normal operational use, when the ring-shaped sealing element is in contact with and provides a complete seal with respect to the periphery of the shaft being sealed, the annular-discoid shape, together with the ribs projecting radially inward, is lost, and the sealing element forms a sealing lip that is conically inclined towards the inside relative to the shaft axis. Viewed in the circumferential direction, this sealing lip is sinusoidally displaced in the axial direction relative to a circular circumferential line. This waviness in the axial direction produces a recirculating effect for the medium to be sealed in the direction of the sealed space. This is caused by the axial deflection of the fluid components between the shaft surface and the sealing lid of the sealing element. However, during normal operational use of this annular sealing element, the position of the sealing lip relative to the shaft surface can experience changes over its service life, due to relaxation of the polymer. In some instances, this can adversely affect the sealing action. However, since the recirculating effect is based on an axial deflection of the fluid components on the shaft, it is necessary to have an unvarying geometric shape and a constant geometric relationship between the seal and shaft over their service life. The working properties of this device are not very satisfactory where long service life is desired, particularly in the case of a stationary shaft where a static sealing action is required.
There remains a need for the further development of a radial shaft sealing ring of this type that exhibits excellent operating properties across a long service life with improved sealing and reduced leakage, both when the shaft is at rest and when the shaft is in rotation.